The present invention relates to method and apparatus which automate imaging studies that require mode changes, such as studies that utilize contrast agents. The present invention is particularly relevant to: stress, echo studies; perfusion studies; coronary flow reserve studies; and the generation of blood flow/volume curves.
A relatively recent advance in ultrasonic imaging is the use of contrast agents to enhance ultrasound returns. Contrast agents are substances which strongly interact with ultrasound waves and return echoes which may be clearly distinguished from those returned by blood and tissue. Contrast agents generally comprise coated gas microbubbles that are stable in the body for a significant period of time. The coating shells serve to protect the gas from diffusion into the blood stream, but at moderately high ultrasound pressure amplitudes the shells of the microbubbles rupture (creating an easily detectable ultrasonic event) freeing the internal gas and substantially eliminating the detectability thereof by incident ultrasound waves.
Contrast agents provide a non-linear behavior in certain acoustic fields. Such behavior is readily detectable by use of known algorithms. Contrast agents are useful for imaging of the body""s vascular system and are injectable through the veins and arteries. They are subsequently filtered from the blood stream by the lungs, kidneys and liver. Contrast agents are currently approved for left ventricular opacification (LVO) and may soon be approved for myocardial perfusion studies.
The present inventors believe that a variety of ultrasound imaging studies could take advantage of contrast agents to obtain various views of the patient. As used herein the term ultrasound imaging study (or more simply imaging study) refers to an examination that requires the creation of a series of ultrasound images (or a series of collection of images such as with cineloops) that each require the ultrasound system, used to obtain the images, to be configured in a different mode. The collection of image settings required to configure the ultrasound system to image in a specific manner is collectively referred to herein as the imaging configuration. Accordingly, each imaging configuration has a variety of associated image settings which control the operation of the ultrasound system monitoring the patient during the imaging study. Some examples of imaging studies that might benefit from the use of contrast agents include stress echo, Left Ventricular Opacification/Myocardial Perfusion studies and generation of blood flow/volume curve studies.
A stress echo study is a safe, noninvasive study that uses ultrasound (sound waves) to evaluate the function and blood flow of the heart in response to exercise. A stress echo study is typically performed by having a patient pedal a stationary bicycle while lying on a bed. Some stress studies are given using a treadmill where the patient""s heart function are continuously monitored for eletrocardiographic changes and also wall motion abnormalities. A variety of devices are used to monitor the patient, including an electrocardiograph machine (ECG), an ultrasound imaging system, a blood pressure cuff and a mask. The ECG records your heart""s electrical activity from information received through electrodes, taped to a patient""s back and chest. The ultrasound imaging system monitors the heart""s activity and provides quantitative and qualitative information about the functioning of the heart. The blood pressure cuff constantly monitors the patient""s blood pressure, while the mask may be used during the study to measure oxygen use.
Sometimes a drug such as adenosine, dobutamine, or persantine is used, instead of a treadmill, to simulate the heart""s reactions to exercise. These drugs are safe and reasonably well tolerated, and are usually only given when the body is unable to perform the stress study, for instance if a patient is particularly out of shape, has lost limbs, or is severely arthritic.
During a stress study, a study giver will gradually increase the speed and incline of the exercise device every two to three minutes while monitoring the patient""s heart through the various devices listed above. The stress study usually lasts between six and ten minutes. Throughout the study,.the heart""s function and/or oxygen flow in response to increased xe2x80x9cchallengesxe2x80x9d to the heart will be closely observed. Stress studies may enable a doctor to estimate the severity of blockages. Further, if the patient has just undergone balloon angioplasty or bypass surgery, a stress study helps doctors monitor the success of the procedure as well as determine an appropriate rehabilitation program. Unusual changes in ECG patterns or blood pressure, and/or unusual shortness of breath or chest pain, are possible symptoms of coronary artery obstruction.
Ultrasound systems enhance stress study by facilitating the detection of ischemia. However, such detection requires the acquisition of multiple views (at least four) during the study. While each of the views is imaged using the same imaging mode, this is still quite a challenge on a moving patient during a rather short time period. U.S. Pat. No. 5,152,290 teaches a method for acquiring stress echo images to facilitate accurate comparisons of views using .a constant acoustic frame rate. The assignee of the present application, AGILENT TECHNOLOGIES INC., has implemented an automated stress package on the SONOS 5500 system that facilitates the collection of ultrasound images during a stress study: Such systems are highly successful for basic imaging procedures where the imaging configurations utilized do not require a mode change.
Contrast agents have the potential to dramatically improve the qualitative and quantitative information obtained during stress echo studies by improving and speeding up visualization of the endocardium. However, the use of contrast agents requires different imaging configurations, e.g. modes of imaging, requiring complex. parametric changes during imaging. For example, a high mechanical index (MI a measure of the power output by an ultrasonic transducer) is-required for good tissue harmonic imaging (one of the standard imaging modes for stress echo studies), while low MI""s are required for LVO contrast imaging. Such a switch requires a battery of parametric changes to the imaging settings making the integration of contrast imaging with stress echo studies unduly complicated. Further, additional modes of contrast imaging are being perfected, including harmonic power Doppler and pulse inversion imaging. Trying to manually integrate such contrast agent imaging modes with the current imaging modes used during stress echo studying is almost impossible because of the complexity of the operator actions required to reconfigure the ultrasound imaging system.
If contrast agent perfusion studies are approved, such studies will face similar problems in that system parameters and imaging modes will have to be modified quickly between: images without contrast agents (employing high MI tissue harmonics); images for LVO (employing low MI, near-field focus, and special detection techniques such as pulse inversion); and images for perfusion (employing high MI and special triggering techniques such as frame rate control, harmonic power Doppler, power modulation, or pulse inversion Doppler). It is anticipated that perfusion studies will require images from at least four viewpoints. It is further anticipated that images using at least three different imaging modes (2D without contrast, LVO with contrast, and perfusion) will be necessary from each view point, making for a total of twelve images with mode and parametric switches in between each image.
Another contrast agent imaging study is current being explored that generates a blood flow/volume curve. The curve is generated by triggering image acquisition based on cardiac triggers and varying the number of beats between cardiac triggers from 1 cardiac cycle to up to 10 cardiac cycles or more. This study requires the use of ultrasound exhibiting a specific set of parameters including frequency, PRF""s, MI, transmit cycles, etc. . . A varieties of factors must be closely controlled during the study:.contrast infusion rate, contrast destruction rate (requiring fine control over the ultrasound signal), triggering, and image optimization. To complicate things, it is likely that each view may require a different contrast agent infusion rate because of view dependent attenuation.
Another type of imaging study that could potentially use contrast agents is a coronary flow reserve study which attempts to identify ischema. Basically, this type of study calls for the location of a coronary artery, which has proven difficult. Once a suitable section of artery has been identified, the artery is monitored at rest and under stress using, among other modes, Doppler. By comparing at rest values with stress values ischema can be quantified. Coronary flow reserve studies have proven difficult to implement without contrast agent. Using contrast agents in conjunction with specialized imaging modes, such as ultra-harmonics, holds the promise of helping the user locate coronary arteries, thereby facilitating coronary flow reserve studies. However, a variety of system settings need adjustment during the study, including Doppler system settings such as scale and gate, making the manual implementation of coronary flow studies improbable due to the difficulty of reproducing the various settings during the course of the study.
In summary, it appears that imaging studies utilizing contrast agents are going to be very complicated and require the rapid changing of imaging modes and parametric information during the study. At the present time, the barriers to acceptance outweigh the clinical benefit of imaging studies incorporating contrast agents. However, this situation is expected to change. Accordingly, the inventors have recognized a need to simplify such studies by automating the rapid changing of imaging modes and parametric information during the study.
An ultrasound system having transmit and receive circuitry that, pursuant to a plurality of image settings, transmits ultrasound signals into a patient, receives echoes from a patient and outputs a signal representative of the echo. Control circuitry is provided that sequentially adjusts the image settings so as to cause the transmit and receive circuitry to have a sequence of imaging configurations during an ultrasound imaging study using contrast agents. A memory may be provided that stores a plurality of state diagrams, each defining a sequence of imaging configurations for a particular imaging study, which are accessible by the control circuitry, wherein the control circuitry accesses a selected state diagram to conduct an imaging study.